fig9

Figure 9. Microneedle base electrochemical insulin sensing. (A) Steps involved in aptasensor operation: (i) Extraction of insulin from ISF, (ii) binding of the extracted insulin to the immobilized aptamer, and (iii) EIS; (B) Electrochemical response of the aptasensor during cortisol detection; (C) Comparison of ∆R_ct (change in charge-transfer resistance) for insulin-specific aptamers and non-specific ssDNA. ^*P < 0.05, One-way analysis of variance; (D) Schematic illustration of the sandwich-type immunosensor. Insulin is sequentially captured through antibody-antigen binding on a MoS₂/Au NP-modified GCE, while the Cu₂O@TiO₂-PtCu/Ab₂ nanocomposite functions as a catalytic label to enhance the electrochemical signal via H₂O₂ reduction; (E) Amperometric responses of the immunosensor toward increasing insulin concentrations (0-100 ng/mL); (F) Nyquist plots illustrate stepwise impedance changes during immunosensor assembly. The error bars in (C) and (F) show the standard deviation. (A-C) Reproduced with permission Copyright 2025, Biosensors and Bioelectronics^[25]. (E and F) Reproduced with permission Copyright 2019, ACS Applied Materials & Interfaces^[128]. ISF: Interstitial fluid; EIS: electrochemical impedance spectroscopy; ssDNA: single-stranded DNA; NPs: nanoparticles; GCE: glassy carbon electrode; BSA: bovine serum albumin.